Battery separator



' To all whoin it may concern:

Patented June 2, 1925.

UNITED STATES PATENT OFFICE.

omvnn w. snows annomrnn o. HENKE, or nnoommo'ron, INDIANA.

sA'r'rnnY snrm'ron,

No Drawing.

Be it known that we, OLIVER W. BROWN and CLYDE O. HENKE, citizens of the United States, residing at Bloomington, in the county of Monroe and State of Indiana, have invented a new and useful Battery Separator, of which the following is a and warp. In our co-pending application,

Serial No. 636,310, filed May 3, 1923, we disclose how it is possible to dry wood separators satisfactorily after their treatment, and such drying is now in commercial use.

It is found, however, that when'the dried treated separator is used in a battery, its electrical resistance is initially considerably higher than is the electrical resistance of the treated separator which has never been dried, and remains so for a very considerable time. This is especially so with certain kinds of wood, such as redwood and Port Orford cedar, though less noticeably so with other kinds of wood.

It is the object of our present inventionto make the electrical resistance of the dried treated wood separator quickly of the same order as that of the undried wood separator upon immersion in the electrolyte, so that the battery using such dried treated wood separators may be put into effective use shortly after being supplied with the electrolyte.

In carrying out. our invention, we provide a supplemental treatment for the wood of the separator after the ordinary pre parator treatment for the removal of wood acids. y this supplemental treatment, we impregnate the pores of the Wood with a substance which is substantially or nearly insoluble in water-,but is readily soluble in the batteryelectrolyte. We preferably obtain this impregnation by precipitation in the pores of the wood, from a reaction in water solution, so that the impregnating substances will remain in the pores until immersion in' the electrolyte.

Application filed -October 10, 1923; Serial No. 667,700.

We have found that by such impregnation, the separators when immersed in the eletcrolyte will within a few hours have an electrical resistance which. is nearly as low as that of the separator which has never been dried. This electrical resistance is much lower than the separator will have if it is not given this supplemental treatment of impregnation by a substance not readily cipitation, so that the woodwill become saturated with such solution. Then we transfer this saturated wood to a solution of a second compound which is to enter into such reaction; which transfer may be made by moving the wood or by drawing off the first solution and substituting the second, The compound in the second solution reacts with the compound in solution in the pores of the wood to produce therein a precipitation of the desired impregnating substance, which upon such precipitation fills or largely fills such pores. The wood may then be washed, if desired, to remove any remaining water-soluble material, leaving the precipitated water-insoluble material within the pores of the wood and thoroughly impregnatin it.

After this impregnation, and a ter the washing ifthat was done, the wood which has thus been treated is suitably dried. This drying may be by the process set forth in our aforesaid application, and preferably ess of drying is not part of the present invention.

soluble .in water, as we have found by. rather" After the wood has been dried, it may 7 be formed into separators, if the separators were not previously formed complete. VVit-h our invention, the impregnation and drying may be either before or after the,

forming of the separators.

\Vhen the dried wood separator thus impregnated is placed in the electrolyteof a storage battery or other electrolytic cell, the water-insoluble substance which was deposited in the pores of the wood is quickly I v dissolved by the electrolyte, and the electrical resistance of the wood separator is within a short time found to be of the order trical resistance of an undried treated wood separator after twenty-four hours immersion in the electrolyte was found to be 0.0014 ohms, While with a similar dried treated wood separator impregnated as set forth the electrical resistance after the same period of immersion was found to be 0.0022 ohms; whereas with a similar dried treated separator which had not been impregnated the electrical resistance after the same period of immersion in the electrolyte was found to be 0.0074 ohms. The figures just given are merely indicative, and vary with different woods and diiierent lengths of immersion. In other words, based on twenty-four hours immersion in the electrolyte, the tests mentioned above show that the dried unimpregnated but treated wood separator has an electrical resistance about five times that of the undried treated wood separator; but that this is reduced to less than one-third 0t that, or to about only one and one-half times the electrical resistance of the undried treated wood separator, if the dried' separator is impregnated in accordance with our invention after preliminary acid-removing treatment but before drying.

There are various compounds which w may use for this impregnation. These in clude the oxide and hydroxide of aluminum, the oxide, hydroxide, and carbonates .of magnesium, and the oxide, hydroxide, and carbonate of beryllium; all of which dissolve in the battery electrolyte by chemical reaction therewith to produce compounds which are not harmful to the battery action. In fact, we may use any compound which is insoluble or nearly insoluble in water but soluble in battery electrolyte, and which includes an element whichis not lower than is aluminum in the electromotive. force series-in other words, a compound having the solubility characteristics above referred to, and including an element which is at least as electropositive as is aluminum. Thus it includes the aforesaid compounds of those magnesium-group elements which have an atomic weight of less than 28, and also includes such compounds of elements which have atomic weights lying between 24 and 28 inclusive.

To obtain the precipitation of the impregnating substance in the ores of the wood, we may use any avai able water-soluble substances which react to produce such impregnating compounds. For instance, the aluminum compounds may be precipitated in the pores of the wood by the reaction of aluminum sulphate with an alkali hydroxide or carbonate; the beryllium compounds by the reaction of beryllium sulphate with an alkali hydroxide or carbonate; and the magnesium compounds by the reaction of ma nesium sulphate with an alkali hydroxi e or carbonate. In attaining this impregnation, the'wood which has been treated to remove the acids may be immersed in either solution first. That is, to impregnate with magnesium carbonate, for instance, it may be immersed first in magnesium sulphate solution, and subsequently in sodium carbonate solution; or it may be immersed first in sodium carbonate solution and then in magnesium sulphate solution.

We are aware that it has been proposed to impregnate treated wooden separators with water-soluble salts, as disclosed in the patent to lVoo'd, No. 1,451,003, granted April, 10, 1923. Wood claimed that such impregnation aided in preventing separators from cracking and warping upon drying. Our invention, of impregnating the treated wood with a substance practically insoluble in water, is not for the purpose of preserving the separators during the drying process, but

is for the purpose of producinga separator which quickly assumes a low electrical re sistance after it is immersed in battery electrolyte. Theimpregnation with water-sol uble salts, as disclosed by Wood, does not produce this desired low electrical resistance of the separator upon immersion in the electrolyte. For comparison, a test made on the same basis as those given above, with a wooden separator treated before drying with a solution of magnesium sulphate as disclosed in the Wood patent, and then dried to leave behind crystals of magnesium sulphate, had after an immersion of twentyfour hours in battery electrolyte an electrical resistance of 0.0128 ohms, as against the resistance of 0.0022 ohms for the separator impregnated with the water-insoluble compound; or approximately five times as high. \Ve cannot give the reason for this ditference, but extensive tests show that it exists, and is of the order indicated by'the example given above. In the tests mentioned, exactly similar separators of red wood were used.

We claim as our invention L'A dried treated wood separator for storage-battery or other electrolytic cells, with the wood impregnated with a substance which is substantially insoluble in water but is soluble inthe electrolyte of the cell.

2. The separator set forth in claim 1, with the addition that such impregnating sub-, stance is a compound of an element at least as electropositive as aluminum.

3. The separator set forth in claim 1, with the addition that such impregnating substance is a compound of a magnesium-group element having an atomic weight below 28.

- 4. The separator set forth in claim 1, with the addition that such impregliatin sub stance is a compound of a metal having an atomic weight between 24 and 28 inclusive.

5. A dried treated wood separator for storage-battery or other electrolytic cells,

the addition that such impregnating sub stance is a compound of magnesium.

7. The process of preparing wood separators for stora e-battery or other electrolytic cells, comprising-treating the wood to remove acids and other substances deleterious to the cell, then subjecting the wood successively to solutions of two compounds which react to form a precipitate in the pores of the wood, and drying the wood subsequent to such precipitation.

8. The process of preparing dried treated wood separators for storage-battery or other electrolytic cells, comprising subjecting the treated wood successively to two reagents which react to form a precipitate in the pores of the wood, and subsequently drying the wood. a

9. The process of preparing dried treated wood separators for storage-battery or other electrolytic cells, comprising immersing the wood successively in solutionsof two com- 10. The process of preparing dried treated wood separators for storage-battery or other electrolytic cells, comprising immersing the wood successively in a solution of a compound of a metal at least as electropositive as aluminum and a solution of a compound which reacts with such metallic compound to form a precipitate soluble in battery electrolyte, and then drying th wood. 4

11. The process of preparing dried treated wood separators for storage-battery or 'other electrolytic cells, comprising immersing the wood successively in a solution of a compound of a metal having an atomic weight between 24 and 28 inclusive and a solution of a compound which reacts with such metallic compound to form a precipitate soluble in battery electrolyte, and then drying the wood.

12. The process of preparing dried treated wood separators for storage-battery or other electrolytic cells, comprising immersing the wood successively in a solution of a compound of a magnesium-group element having an atomic weight below 28 and a solution ofa compound which reacts with such metallic compound to form a precipitate soluble in battery electrolyte, and then drying the wood.

In witness whereof, we have hereunto set our hands at Bloomington, Indiana, this 6th day of October, A. 1). one thousand nine hundred and twenty-three.

OLIVER W. BROWN. CLYDE O HENKE. v 

